The present invention relates to a pan granulation method for pan granulating pellets or granules and more particularly, the present invention relates to a wet granulation method for granulating fertilizer and other materials into industrially useful pellets or granules.
One of the greatest limitations existing in the granulation art is centered on the fact that known processes require a seeding agent in order to achieve the proper conditions for material accretion to result in a pellet or granule. By making use of a seed, the resulting granule is adversely affected in two key properties; roundness and cross sectional uniformity. Typically, seeding material is not round and as the precursor particle, the result is irregular initial feedstock accretion which, in turn, forms an out-of-round particle upon which further material accretes. A further detriment from this results in terms of nonuniform particle density.
Methodology is required for synthesizing a granule in the absence of seed material and which is round, tightly packed with a uniform homogeneous cross section and capable of eliminating hazards associated with fertilizer granule production.
One of the latest issued patents in the art to which the present invention relates is U.S. Pat. No. 5,460,765, issued to Derdall et al., Oct. 24, 1995. The reference teaches a process for pan granulating a particulate material. Based on the teachings of the Derdall et al. reference, a final particle size distribution that is achievable by practicing the invention is between about xe2x88x925 mesh to about +10 mesh. In order to initiate the process, the Derdall et al. process is limited to the introduction of a seeding material typically between about 14 mesh and +28 mesh. This is required in order to control the granule growth and as indicated in the Derdall et al. disclosure, seed minimizes mutual agglomeration and results in high yields being obtained. The Derdall et al. reference further indicates that the proper sizing of the seed is fundamental to the operation of the process for granulation in order to have product yields exceed 90%. Reference is made in the disclosure that a seed core in the range of 14 mesh to +35 mesh is required in order to achieve a steady state and maintain uniform size distribution of between 8 mesh to +6 mesh.
The Derdall et al. process, although a meritorious procedure, did not recognize the limitations of employing a seeding agent or the need for controlling the dust generated during granulation which not only creates an unhealthy environment for workers, but more seriously, results in a potentially explosive environment. This is evident from the teachings of Derdall et al., particularly at column 3, beginning at line 24, wherein it is stated:
xe2x80x9cIt may be more difficult to keep the granulation steady or stable with fine seed, such as xe2x88x9235 mesh.xe2x80x9d
The difficulty to which the Derdall et al. disclosure alludes is directed to cycling which is an inherent problem with pan granulation processes. If the size distribution of the seeding agent is not constant, then the process will not stabilize and effectively xe2x80x9ccyclesxe2x80x9d as is known to those skilled in this art. The result of this is that larger formed granules on the pan effectively destroy the smaller particles. This, of course, defeats the purpose of the pan granulation to generate particles.
Furthermore, at line 36 in column 3, the disclosure indicates that:
xe2x80x9cFine seed sizes can be used, such as +35 mesh, but a point is reached where over-seeding or nucleation occurs easily and causes the final product yield to drop down.xe2x80x9d
It is also indicated at column 3, beginning at line 45 that:
xe2x80x9cSeed material in the range of 20 mesh is the best single point for each of control and uniformity of product size distribution . . . xe2x80x9d.
As is known, the larger the mesh numerical value the smaller the micron size of the particle. The following mesh sizes correspond to the stated micron sizes:
Based on the teachings of the Derdall et al. disclosure, mesh sizes greater than +35 cause potential nucleation problems and result in a final product yield to decrease. With the technology disclosed, infra, it has been found that by using a fine powder of between xe2x88x9235 mesh to +150 mesh, that a superior quality product can be formed in high yield and typically in the range of a greater than 90% yield.
In the present application the size distribution of the nucleating material is between 35 mesh and +150 mesh which corresponds to micron size less than 590 xcexcm and 105 xcexcm, respectively. Nowhere in the prior art is a powdered nucleating agent in this size distribution disclosed for the purpose of forming a uniform granule in the size distribution of xe2x88x928 to +4 mesh. Advantages have been ascribed to this process and one of the most attractive advantages is that the granule or pellet has an enormous break strength and a uniform cross section. It has been found by practicing the present invention, that break strengths in the range of 1 to 4 kgs or greater have been achieved.
In the Derdall et al. disclosure, at column 3, beginning at line 33 it is stated:
xe2x80x9cSeed of large size forms granules of very poor strength.xe2x80x9d
If one considers these teachings in light of the size of the nucleating agent provided herein, the admissions made in the Derdall et al. disclosure would clearly go against the appeal of using a seeding agent in the size range as clearly taught by Derdall et al. The instruction in Derdall et al. indicates an ideal seeding agent size is 20 mesh (supra); the instant application uses a powder having a particle size between 75-750% smaller than Derdall et al. and yet achieve very desirable results.
In Statutory Invention Registration H1070, authored by Harrison et al., Jul. 7, 1992, a method for granulating potash materials is disclosed. The process involves the conversion of particulate potassium sulfate or potassium chloride by agglomeration using a conventional rotary drum granulator, pan granulator or other conventional granulating device.
In the disclosure of this document, there are no specific teachings regarding the elimination of a seeding agent, feedstock size or other important factors related to process control in order to generate superior quality granules having commercial viability. Further, the process is clearly an agglomeration process. It is known that agglomeration typically involves the aggregation of colloidal particles suspended in a liquid into clusters or flocs. These clusters or flocs have varying degrees of interstices and are loosely bound (Hawley""s Condensed Chemical Dictionary, eleventh edition, 1967).
As a particularly advantageous feature of the present invention, the methodology herein facilitates sulfur granulation. With the effectiveness of air pollution regulations, it has now become necessary to augment the soil with sulfur due to deficiencies. As is generally known in agricultural science, sulfur fertilization increases crop yield and quality and further has an effect on nitrogen processing by plant matter. This processing is, in turn, related to protein synthesis, nitrogen fixation, photosynthesis and disease resistance.
Wet granulation is inherently complicated, since irregular particle crystallography is inherently difficult to control. Wet powder is not uniform and this leads to non-uniform accretion, over nucleation and eventual breakdown of the process. For these reasons among others, the art has not realized an effective and viable process for wet granulation.
Boeglin et al. in U.S. Pat. No. 3,853,490, discloses a granulation method for granulating potassium sulfate. The method involves the use of large particle starting material xe2x88x926 +65 mesh (50%), xe2x88x92200 mesh (10% to 30%) and the remainder comprising xe2x88x9265 +200 mesh. In the disclosure it is stated that the granulation is carried out in conventional granulating equipment, however, there is no discussion concerning process control difficulties associated with pan granulation of the product. It is known from Derdall et al that significant difficulties are encountered in keeping the granulation steady even with seed material in the size range of +35 mesh. The most difficult problem is controlling xe2x80x9ccyclingxe2x80x9d where the larger particles destroy the smaller particles. The Boeglin et al. reference would therefore appear to be directed solely to a drum granulation process where the complications inherent with pan granulation are not encountered.
In U.S. Pat. No. 3,711,254, issued to McGowan et al., there is discussed a process for granulating potash. The disclosure of the document only provides a cursory teaching of granulation and includes pan and drum granulation within the same process.
Kurtz, in U.S. Pat. No. 5,322,532, discloses a sodium bicarbonate blast media. The blast media comprises an agglomeration of sodium bicarbonate and sodium sesquicarbonate. The reference does not set forth any details with respect to any other formulation process apart from agglomeration and lacks instruction regarding any other material for augmentation.
Other patent documents of only marginal relevance include the following U.S. Pat. Nos.: 4,371,481; 4,131,668; 4,264,543; 5,108,481; 3,206,508; 3,206,528; 4,344,747; and, 5,124,104.
The prior art, when taken singly or collectively, is deficient any clear teachings regarding the preparation of fertilizer, blasting, deodorizer or water softener granules having the following commercial and industrial advantages:
a) uniform cross section;
b) tightly packed feedstock;
c) absence of a seed or crystal core;
d) increased break strength relative to the prior art;
e) material homogeneity throughout the granule; and
f) greater quantity of feedstock material per granule
There has been a long felt need for granules having these desirable properties and for methodology to effect synthesis of such products; the present invention addresses these needs in an elegant and efficacious manner
One object of the present invention is to provide an improved method for generating a variety of industrially useful particles or granules, which particles are devoid the drawbacks of the prior art techniques.
A further object of one embodiment of the present invention is to provide a wet granulation method for granulating a feedstock into granules, comprising the steps of:
providing a first feedstock having about 99.9% particle size of xe2x88x92150 mesh of said 99.9% particle size of xe2x88x92150 mesh about 90% comprising a particle size of xe2x88x92200 mesh;
providing a binder material having a moisture content;
contacting said first feedstock with said binder;
forming a pre-moistened mixture of said binder, said first feedstock and said moisture;
introducing said pre-moistened mixture onto a pan granulator containing a second feedstock different in composition from said first feedstock;
maintaining moisture conditions on said pan where the moisture content on said pan is between 1.5% and 11% by weight; and
forming first granules on said pan directly from contact of said pre-moistened mixture and said second feedstock in the absence of said material.
In the present invention, the maintenance of moisture on the pan and in the product substantially prevents dust formation during product synthesis. This is augmented by the addition of oil e.g. mineral, vegetable, seed, synthetic, etc. to the final product. As a further feature, plant nutrients, growth regulators, minerals, time release compositions and suitable bacteria may be included in the granules. In terms of the nutrients, suitable examples include nitrogen, phosphorous and potassium; the growth regulators may be herbicides, pesticides, hormones; the minerals will vary depending on soil and environment conditions, but may include copper, boron and other metals; the time release materials may be selected to release the sulfur only at specific times during the growth cycle of the plant, crop, etc.; bacteria may be selected from a diverse variety depending on the specific requirements of the user. To this end, sulfur oxidizing bacteria may be selected, disease combating bacteria to reduce the vulnerability of the crop etc.
As another feature of the present invention, the technology can be easily employed in the granulation of pellets/granules used in other fields outside of the agricultural sciences. One such field is the blasting art. In this field, it is well known that sodium bicarbonate is a useful blasting medium in view of the copious benefits associated therewith. The bicarbonate is useful, but the crystals are such that high efficiency in coating removal from a substrate is not entirely practical. The present technology facilitates granulation of the bicarbonate with further crystalline materials to augment the abrasiveness of the granule.
The important inventive concept of the present invention is the ability to generate particles/granules in the absence of a seeding agent. In this manner, the process can be loosely referred to as a pan nucleation process; the process proceeds generally as crystallization, i.e., a nucleation site accretes the surrounding material. With the present technology, the pan rotation and binder assist in the material accretion around the nucleation site to produce a tightly packed granule with high feedstock content.
As a further object of one embodiment of the present invention, there is provided a wet granulation method for granulating a feedstock into granules, comprising the steps of:
providing a first feedstock having about 99.9% particle size of xe2x88x92150 mesh of said 99.9% particle size of xe2x88x92150 mesh about 90% comprising a particle size of xe2x88x92200 mesh;
providing a binder material having a moisture content;
contacting said first feedstock with said binder;
forming a pre-moistened mixture of said binder, said first feedstock and said moisture;
introducing said pre-moistened mixture onto a pan granulator containing a second feedstock different in composition and size from said first feedstock in a size distribution of between xe2x88x9235 mesh and +150 mesh;
maintaining moisture conditions on said pan where the moisture content on said pan is between 1.5% and 11% by weight; and
forming first granules on said pan directly from contact of said pre-moistened mixture and said second feedstock in the absence of said material.
Having thus described the invention, reference will now be made to the accompanying drawing illustrating preferred embodiments.